The use of amorphous gels and precipitates as support material for polymerization catalysts is known. For example, aluminophosphate gels and precipitates have often been used for such support materials. In some cases, the support was improved by incorporating silica into the aluminum phosphate support.
While aluminophosphates have long been known, along with their methods of preparation, such aluminophosphates have not as yet achieved commercial success. Part of this is believed to be that the prior art aluminophosphates lacked a combination of physical properties which have been found to characterize superior polymerization catalysts. It is the combination of a high macropore volume of at least 0.1 cc's per gram plus a fragmentation potential (to be defined below) of preferably 30 to 60 plus a preferred mesopore volume of 0.3 to 0.8 cc's per gram which particularly characterize the superior polymerization catalysts. In two prior inventions of Applicants (Pecoraro and Chan, U.S. patent application Ser. No. 08/742,794; Auburn and Pecoraro, U.S. patent application Ser. No. 08/741,595), which are incorporated herein by reference, a new aluminophosphate with both high macropore volume and a fragmentation potential about 30 was developed which was also both physically and thermally stable. It is believed that the presence of sheets of aluminophosphate in the microstructure results in the packing of the microstructures in such a way that a high macropore volume and a high fragmentation potential are achieved along with physical and thermal stability.
In another related invention by Applicants (U.S. application Ser. No. 08/961,825, Auburn, Pecoraro and Chan), which is a continuation-in-part of Ser. Nos. 08/741,595 and 08/742,794 discussed above, and which is also incorporated by reference herein, a silica-modified, amorphous aluminophosphate composition which like the previous inventions exhibits a microstructure of sheets and exhibits spheres of silica-modified aluminophosphate as well.
The use of silica alone or the combination of silica with other oxides such as alumina or titania or vanadia to form such amorphous compositions for use as polymerization catalyst support material is also known. Previously, the microstructure of such supports primarily contained small particles. As a result of this small particle structure, it was difficult to tailor the materials over a wide range of pore sizes, distributions and volumes, and of acceptable fragmentation characteristics.
It would be desirable to find silica support materials which could be used over a wide range of pore sizes, distributions and volumes and of acceptable fragmentation characteristics.
The present invention has achieved such materials. The present invention has achieved high surface area, amorphous silicas which surprisingly form a continuous network matrix, rather than the typical small particles found in conventional amorphous silicas. Furthermore, the pore size and the distribution and volume of the pore size can be tailored over a wide range.
Surprisingly, also, the present invention achieves an amorphous SiO.sub.2 base composition with a non-particulate, dense, network matrix and encapsulated less dense, non particulate regions with true macropores. In one embodiment, the present invention also comprises a sheet-like microstructure.